1. Field of the Invention
The present invention relates to a slope detection method, and an information detection/writing apparatus using the method.
The present invention is particularly suitable for an information processing apparatus, an information processing method, and a slope correction method, which utilize a scan type probe microscope (to be abbreviated to as an SXM hereinafter) having a mechanism for correcting a slope between a scan plane of a probe and a record medium surface.
2. Related Background Art
In recent years, along with expansion of the information-oriented society, large-capacity memories have been developed. Recently, a recording/reproduction apparatus, which uses a scan type tunnel microscope (to be abbreviated to as an STM hereinafter), has appeared (e.g., Japanese Patent Application Laid-Open No. 61-80536, U.S. Pat. No. 4,575,822, and the like). An STM developed by G. Binnig et. al. [G. Binnig et. al., Helvetica Physica Acta, 55, 726 (1982)] is a method of observing a surface condition of a sample by utilizing the fact that a tunnel current flows when a voltage is applied between a metal probe (probe electrode) and a conductive sample, and they are caused to approach each other to a distance of about 1 nm. This current is very sensitive to a change in distance between the probe and the sample. Thus, the distance between the probe and the sample is measured by scanning the sample while maintaining a constant tunnel current, or a change in tunnel current, obtained when the sample is scanned while maintaining a given distance, is measured, thereby detecting the surface condition of the sample. At this time, a resolution in an in-plane direction is about 0.1 nm. Therefore, upon application of the STM technique, high-density recording/reproduction on the atomic order (on the order of subnanometers) can be attained (e.g., Japanese Patent Application Laid-Open Nos. 63-204531, 63-161552, 63-161553, and the like). On the other hand, along with development of the STM technique, various techniques (i.e., SXM) for measuring a surface condition of a sample by scanning a probe on a sample surface while detecting various other interactions (not limited to a tunnel current) depending on a distance between a probe and a sample, have been proposed. When the SXM is utilized, high-density recording/reproduction can be attained in the same manner as a case utilizing the STM.
As described above, high-density recording/reproduction can be attained in principle by utilizing the SXM technique. However, in practice, various problems remain unsolved. The problems in the SXM will be described below using the STM as an example.
First, a probe must be scanned to be parallel to a record medium surface. When this condition is not satisfied, i.e., when a record medium is sloped and placed on a sample table, an observed surface pattern may be distorted, the probe may collide against the record medium surface, or an uncontrollable state may occur since the probe is too far from the record medium surface. When a scan range (a region used for recording information) is relatively small, and a moving amount of the probe in a vertical direction (to be referred to as a Z axis direction hereinafter) caused by the slope of a record medium falls within a Z-axis direction fine-movement control range of the probe (e.g., 1 .mu.m or less), only the moving amount of the probe caused by the actual structure of the record medium surface can be removed from the moving amount of the probe using an electrical filter. In fact, an STM apparatus is equipped with filters for removing various frequency components. Japanese Patent Application Laid-Open No. 2-147803 proposes an STM apparatus, which comprises a mechanism capable of rotating a sample so as to solve the above problem. However, according to these methods, when a recording region is sufficiently large or when a record medium is large, the moving amount in the Z axis direction of the probe forced by the slope of the record medium may often exceed a control range of the probe. Even if the moving amount in the Z axis direction of the probe does not exceed the control range amount, unless a plane where, e.g., the tip of the probe is moved during probe scan, i.e., a direction of a scan plane (to be referred to as an X-Y plane hereinafter) of the probe, is parallel to a direction in a record medium plane (to be referred to as an X'-Y' plane hereinafter), the moving distance of the probe in the X-Y plane direction becomes different from the real space distance on the X'-Y' plane. Therefore, a noncoincidence (non-parallelism) between the X-Y plane and the X'-Y' plane may often impair recording/reproduction precision.
Second, in a recording/reproduction method utilizing the STM, it is indispensable to control the distance between a probe and a record medium with a precision on the order of submicrons. In this case, a piezoelectric element is normally used in distance control. However, the operation speed of the piezoelectric element has an upper limit of about 1 MHz. Therefore, when the STM technique is used in recording/reproduction of, e.g., image information requiring a high transfer speed, a plurality of probes must be inevitably used. For example, Japanese Patent Application Laid-Open No. 62-281138 proposes a technique for improving a recording/reproduction speed using a plurality of probes (multi-probes). In this case, for the same reason as that described in the above paragraph, it is expected that the scan planes of all the probes are adjusted to be parallel to the record medium surface. However, a specific method of attaining such adjustment has not been proposed yet.